The present invention relates generally to blood pressure monitoring, and more particularly to a blood pressure monitoring pad assembly which is especially designed to take the blood pressure of a patient at a supraorbital artery and to methods for using the pad assembly.
The blood pressure monitoring pad assembly of the present invention is designed for use with oscillometric blood pressure monitoring techniques which are well known in the art. In U.S. Pat. No. 5,230,342, which is incorporated herein by reference, techniques are disclosed for utilizing the supraorbital artery of a patient to measure the blood pressure of the patient along with a blood pressure monitoring pad assembly for use in implementation of these techniques. The blood pressure monitoring pad assembly of the present invention represents an improved version of a pad assembly for use with a supraorbital artery of a person. Techniques for using the improved monitoring assembly of the present invention are also disclosed herein.
FIGS. 1 and 2, taken directly from the '342 patent, are diagrammatic illustrations of a prior art blood pressure monitoring pad system which is generally indicated by the reference numeral 10. The system includes a blood pressure monitoring pad assembly 16 including a pressufizable pressure transducing bladder 18 mounted to a larger and more rigid bladder backing 19. A pad 20 has an adhesive backing 22 against which bladder 18 and backing 19 are fixedly mounted. The pad 20 has an outermost configuration which, when applied to the patient in accordance with a method of the patent, properly positions bladder 18 in order to locate and access a supraorbital artery. The assembly is adhesively attached to the forehead of the patient by adhesive backing 22 to be held in the proper position for the duration of the monitoring procedure.
While the blood pressure monitoring pad assembly, as depicted in FIGS. 1 and 2, does permit measurement of the blood pressure at the location of the supraorbital artery and is generally satisfactory for its intended purpose, there are several particular aspects of this assembly that can be improved upon, as will be discussed below.
One such improvement relates to the pressurization of the bladder which causes a force to be directed outwardly from the patient's skin in response to the inward force of the bladder against the skin. This outward force is transferred from the side of the bladder opposite the skin to backing 19 and pad 20. The outward force is applied directly to adhesive backing 22 from pad 20 and thereby to the adhesive bond between the pad assembly and the skin on the patient's forehead. The pad assembly itself is internally constructed in a manner such that the adhesive bond between backing 19 and pad 20 is typically quite strong requiring a force significantly greater than that caused by pressurization of the bladder to break it. The weakest and least reliable bond forming part of the pad assembly is generally the bond between the pad assembly itself and the biological skin on the forehead of the patient. The force which is applied to this adhesive bond by pressurization of the bladder is a peel force. Traditionally adhesives are more resistant to shear forces than peel forces. Once the peel has begun, less force is typically required to propagate the peel. This bond is therefore predisposed to failure in a generally gradual manner in which the bond has a tendency to begin to separate immediately adjacent to the bladder. With repeated pressurization cycles, continuous pressurization or overpressurization, the bond between the skin and the pad assembly is likely to continue to separate.
Separation of the pad assembly from the skin forms an additional space surrounding the bladder in which the bladder is able to freely inflate and deflate during pressurization cycles and, in fact, the bladder has a tendency to fill this additional space during pressurization before applying a significant downward force to the skin whereby to engage the target artery. If the additional space is permitted to reach a large enough volume relative to the bladder, the bladder will be rendered unable to properly engage the skin and the target artery below. Upon continued separation of the adhesive bond between the pad assembly and the skin, the pad assembly may become completely detached from the skin.
An obvious solution to this problem is to use a very strong adhesive to bond the pad assembly to the skin. The adhesive presently in use is one of the strongest available and it is a concern that a stronger adhesive could possibly cause discomfort or, in some cases, even trauma.
A second possible area of improvement of the pad assembly shown in FIGS. 1 and 2 resides in the fact that it is relatively rigid in order to properly support the bladder against the forehead at the location of the supraorbital artery. Since the forehead of most individuals is relatively planar vertically, the pad assembly is capable of conforming to the forehead from top to bottom at the location of the supraorbital artery. Conforming to the curvature of the forehead horizontally, that is, from side to side is a much more difficult matter using the pad assembly as shown, since the horizontal curvature is much less planar. It has been found that the horizontal curvature of the forehead of typical individuals about a vertical axis can vary by as much as a factor of two to one. Due to the fact that the pad assembly is relatively rigid, upon conforming it to an individual's forehead, stress is created within the pad assembly. The greater the curvature of the individual's forehead the greater will be the stress induced within the pad assembly upon application to the subject's forehead. This stress may, in and of itself, lead to a failure of the adhesive bond between the monitoring pad assembly and the skin of the forehead and, in combination with the stress upon the adhesive skin bond due to pressurization of the bladder, can lead to premature failure of the bond with the skin.
It is desirable, in view of the prior art discussed above, to provide a blood pressure monitoring pad assembly for use with a supraorbital artery of a person which will remain operationally attached to the person's forehead and functional for a desirable period of time while still providing for the comfort of the person and, further, to provide a pad assembly which is sufficiently rigid when in use to properly support the bladder during pressurization and yet is sufficiently flexible during the application of the pad assembly to the person's forehead to conform to the shape of the person's forehead at the location of the supraorbital artery, even in cases of relatively sharp horizontal curvature of the forehead about the vertical axis.